The invention relates to a compaction head of a production machine for reinforced concrete pipes, comprising a smoothing cylinder non-rotatably mounted on a drive shaft, for smoothing the inside of a concrete mixture that has been filled into a vertical mold, and a covering wall of the smoothing cylinder, the covering wall being mounted separately from the smoothing cylinder and being connected to it by means of a drive mechanism, and on which the rolls for the radial compaction of the concrete mixture are mounted rotatably with respect to the covering wall and axis-parallel with respect to the drive shaft and, together with the covering wall, can be driven at a specified orbiting speed about the axis of the drive shaft, such that the direction of rotation of the rolls about their own axis is opposite to that of the covering wall about the axis of the drive shaft.
With a known compaction head of this type (DE 27 38 944 A1), the rolls which effect the compaction are put into rotational motion only by rolling off, like drag rolls, with the rotation of the covering wall of the smoothing cylinder of the concrete, but without being driven directly. The rolls thus push the fresh concrete in front of them like a bow wave, so that the compaction of the concrete is not free of torsion, and is stronger at the rear side, as viewed in the direction of motion, of the steel wires of the reinforcing cage than on the front side of the steel wires. The consequence of this is cracks in the finished concrete pipe.